The invention relates to a method of recording information on a record carrier having a recording layer of a thermomagnetic type, a pattern of magnetic domains having a first and a second direction of magnetization being formed in the recording layer by scanning the recording layer with a magnetic field which is modulated depending on an information signal and at the same time, by applying radiation, heating the recording layer locally in the area being scanned to a temperature above a write temperature, above which temperature the magnetization of the recording layer assumes a direction dictated by the magnetic field.
The invention further relates to a magneto-optical recording device for carrying out the above method, which recording device comprises a magnetic-field modulator for scanning the recording layer of the record carrier with a magnetic field which is modulated depending on an information signal, an optical system for applying, by means of a radiation beam, radiation energy to that portion of the recording layer which is scanned by the magnetic-field modulator in order to locally heat the scanned portion to a temperature above a write temperature, above which write temperature the magnetization of the recording layer assumes a direction dictated by the magnetic field.
Such a method and device are described in "Philips Technical Review", Vol. 42, no. 2, pp. 38-47. In said Review it is stated that it is, in principle, possible to form the pattern of magnetic domains by scanning the recording layer with a modulated magnetic field and at the same time heating the scanned portion with a constant-intensity laser beam. At the location of the heated portion the record carrier is then magnetized in conformity with the direction dictated by the modulated magnetic field. After cooling the magnetization of the record carrier persists, yielding a pattern of magnetic domains of opposite directions corresponding to the information signal.
The problem associated with this method, as stated in the above magazine, i.e. an inadequate speed of reversal of the magnetic field, has now been solved. For example, the non-prepublished Netherlands Patent Application no. 8702401 which corresponds to U.S. application Ser. No. 162,827 filed Mar. 3, 1988, now abandoned in favor of U.S. application Ser. No. 253,797 filed Oct. 4, 1988 now abandoned in favor of U.S. application Ser. No. 704,659 filed Jul. 20, 1991, describes a magnetic-field modulator which provides an adequate speed of reversal of the magnetic field. Since the above problem has been solved, the recording method described in the foregoing has become very attractive, because it enables previously recorded information to be readily overwritten without an additional erase operation being required.
The information is read via the rotation of the direction of polarization upon reflection of linearly polarized light. The read quality depends on the signal-to-noise ratio of the signal being read. The noise in the read signal comprises three major noise components, namely; disc noise, resulting from imperfections of the disc; read noise resulting from imperfections in the read process; and write noise resulting from imperfections in the write process.
In the meantime the attainable quality of the discs and that of the read processes have been improved to such an axtent that during reading of these discs the write noise is predominant. Therefore, if a further improvement of the signal-to-noise ratio of the read signal is required, improvements in the write process aimed at reducing the write noise being must be pursued.